This invention relates to improvements in push-in easy opening closures and more particularly to resealable pressure releasing closures of the type suitable for can ends containing carbonated beverages.
Australian Patent Application No. 35318/78 (incorporating provisional specifications PD 0416, PD 0848 and PD 1840), U.S. Pat. Nos. 4,105,134 and 4,155,480 Debenham et al, the disclosures of which specifications are incorporated into this specification by cross reference, describe various forms of resealable pressure releasing closures designed to improve the opening characteristics of can ends for highly carbonated beverages. The closures operate on the principle that by enabling the pressure releasing closure to reseal in the absence of a digitally applied push-in force, the pressure within the can may be released gradually, for example, in short bursts, in the event that the contents of the can tend to gush or spurt. The closures described in the above specifications are constructed in combination with the surrounding portions of the can end to prevent deflection of the closure by an amount at which the yield point of the metal at the connection between the closure and the can end will be exceeded, whereby the tab springs back to at least a substantially closed position when the push-in force is released.
It has been found that by making certain design changes to the resealable pressure releasing closures disclosed in the above applications, and particularly those of the general type shown in FIGS. 17 and 18 of Application No. 35318/78 and FIGS. 5 and 6 of U.S. Pat. No. 4,155,480, substantial improvements in the resealing properties of the closures may be achieved while retaining design features which maintain the commercial attractiveness of the closures.